1. Field of the Invention
This invention relates to photopolymerizable compositions comprising a vinylic compound, a sulfur-containing compound and an .alpha.-diketone.
2. Discussion of the Background
Photopolymerization is used in various fields. For example, print materials, photosensitive agents used in reproduction, printed wirings, integrated circuits, and image formation for precision fabrication, such as shadow masks, as well as paints, printing inks and adhesives, all rely on photopolymerization.
Photopolymerization is also used in dentistry, for example, photopolymerizable materials are used in association with tooth fillers (composite resins or the likes), tooth sealing materials and dental adhesives, as well as in the production of tooth decay preventive fillers, tooth crowns and dentures
A case in point with regards to the photopolymerizable compositions described above, is a photopolymerizable composition curable with visible light or UV-rays described in Japanese Patent Publication No. 10986/1979. This photopolymerizable composition comprises a photosensitive catalyst containing a photosensitive agent/reducing agent as the photo-initiator. This photo-initiator is made up of components (a) and (b). Component (a) has at least one photosensitive agent represented by the following formula: ##STR1## where;
X represents &gt;C=0, &gt;CR.sub.5 R.sub.6 or &gt;CR.sub.7 OR.sub.8 ; and R.sub.5 -R.sub.8 may be either identical or different and each represents a hydrogen or a hydrocarbon group; n is 0 or 1; and the groups A which may be either identical to each other or different from each other represent an unsubstituted hydrocarbon group or a substituted hydrocarbon group. Both of the groups A may be coupled directly, joined by way of a bivalent hydrocarbon group, or alternatively, both of the groups A may form together a condensed aromatic ring. The group A may represent an unsubstituted aromatic group or a substituted aromatic group if n is 1 and X is &gt;CR.sub.5 R.sub.6 and if n=0. Component (b) has at least one reducing agent represented by the formula: EQU NRRR
where each R may be identical or different with respect to each other; and each R represents a hydrogen, an unsubstituted hydrocarbon group, a substituted hydrocarbon group or a group in which two R form a ring together with N. Three R do not simultaneously represent substituted hydrocarbon groups and N is not coupled directly to the aromatic group. The photopolymerizable composition also contains an unsaturated polymerizable ethylenic material. Particularly preferred examples of this unsaturated polymerizable ethylenic material, for the photosensitive agent are: biacetyl, benzil, benzophenone, camphorquinone and the like. For the reducing agent preferred examples are: trimethylamine, tripropylamine, dimethylamine, propylamine, N,N'-dimethylaniline, N-methyldiphenylamine, ethylenediamine, hexamethylenediamine, dimethylaminoethyl methacrylate, piperidine and the like.
Although the materials using these photoinitiators can be rapidly cured via photoirradiation, they suffer several drawbacks. The curing products are significantly colored (mostly yellowed), they show significant aging (i.e. change in color tone) upon exposure to sunlight or water, and products with low strength are produced.
Accordingly there is a particular need for a novel photopolymerization composition which may have wide application and which does not suffer from the drawbacks outlined above.